Filamentary structure of plasma produced by compression of puffing deuterium by deuterium or neon plasma sheath on plasma-focus discharge

Abstract

The present experiments were performed on the PF-1000 plasma focus device at a current of 2 MA with the deuterium injected from the gas-puff placed in the axis of the anode face. The XUV frames showed, in contrast with the interferograms, the fine structure: filaments and spots up to 1 mm diameter. In the deuterium filling, the short filaments are registered mainly in the region of the internal plasmoidal structures and their number correlates with the intensity of neutron production. The longer filamentary structure was recorded close to the anode after the constriction decay. The long curve-like filaments with spots were registered in the big bubble formed after the pinch phase in the head of the umbrella shape of the plasma sheath. Filaments can indicate the filamentary structure of the current in the pinch. Together with the filaments, small compact balls a few mm in diameter were registered by both interferometry and XUV frame pictures. They emerge out of the dense column and their life-time can be greater than hundreds of ns. V C 2014 AIP Publishing LLC.

Evolution of the small ball-like structures in the plasma focus discharge

“…The diameter of the pinholes was 80 m and the magnifi cation ratio was equal to 10. Therefore, the spatial inaccuracy of the gained frames was about 0.8 mm [1,2]. The angle between the optical axis of the MCP detector and the main interferometric beam was 45°.…”

“…The short description of the ball-like structures observed in shot #10080 and #10122 was presented in a paper [1]. In that paper, it was observed that the ball-like structures occurred at the imploding plasma shell boundary, the lifetime of the structures could be longer than 200 ns, the maximum electron density in the center of such structures was about 10 25 m -3 .…”

“…It should be noted that such ball-like structures were observed in two experimental campaigns when we also observed many fi ne fi lamentary structures in the dense plasma column [1]. Further more detailed descriptions of the ball-like structures are in the following sections: experimental results, evolution of the ball-like structures, discussions, and conclusions.…”

“…More detailed information about diagnostics applied at the PF-1000 facility was given in earlier papers [1,2].…”

“…The author suggested that the internal region without clear pattern of fringes was caused by internal turbulent behavior with velocities determined by the duration of the diagnostic laser beam above 10 6 m/s. Structures decayed by absorption in the expanding column with the decreasing of the electron density or by ejection of a plasma jet [1].…”